Draft: Characterization of Development in Columbia River Prolarval Eulachon, Thaleichthys pacificus, Using Selected Morphometric Characters

Active spawning of eulachon, Thaleichthys pacificus, has been observed in various tributaries of the Lower Columbia River, including the Cowlitz River, the Kalama River, the Lewis River, and the Sandy River (Smith and Saalfeld 1955). However, little is known about the spawning distribution of eulachon in the Lower Columbia River mainstem itself.

Catches of very recently hatched eulachon larvae in plankton net hauls might indicate proximal spawning grounds and hence provide a useful tool for mapping and defining spawning habitat distribution in the mainstem Columbia River. To achieve this, developmental observations from larvae of known ages are required to provide a baseline against which larval assemblages collected in the field can be compared.

Upon hatching, larvae are incorporated into the drift and, depending on local current velocities, are presumably transported substantial distances from their spawning grounds in relatively short periods of time. For an aging methodology to be an effective tool in pinpointing spawning areas, short-term developmental changes - measured on an hourly time scale - must be identified.

Eulachon larvae have been successfully propagated by several workers for various studies that include: spawning substrate preference (Wendler 1937); assessment of possible population heterogeneity in the Lower Columbia River and its tributaries (Delacy 1963); and effects of temperature on incubation periods (Smith and Saalfeld 1955). Parente (1970) provides a pictorial record and discussion of egg and (to a limited extent) larval development. However, a systematic, quantitative assessment of eulachon larval development has not been previously described as it has for other, related species such as the Rainbow smelt, Osmerus mordax, (Cooper 1978). Given the lack of information regarding eulachon larval development our goal was to artificially propagate larvae, establish a time/temperature dependent developmental baseline and subsequently evaluate the efficacy of our proposed methodology.